1. Field of the Invention
The present invention relates to a rotary damper for applying damping forces to a lid, a door, or the like when it is opened and closed.
2. Description of the Prior Art
One conventional rotary damper for applying damping forces to a lid, a door, or the like when it is opened and closed is disclosed in Japanese patent No. 2581655, for example. As shown in FIG. 20 of the accompanying drawings, the disclosed rotary damper has a rotatable member 5 rotatable about its own axis. When the rotatable member 5 rotates counterclockwise to open a lid connected thereto, for example, a valve body 22 interposed between a vane 16 disposed on the outer circumferential surface of the rotatable member 5 and the inner circumferential surface of a cylindrical casing 2 moves clockwise with respect to the vane 16, producing a fluid passage for a fluid to pass between the valve body 22 and the vane 16 through recesses 101, 102 defined in at least one of the valve body 22 and the vane 16. Therefore, when the lid is opened, since almost no resistance is developed to the fluid flowing through the fluid passage, the torque generated by the rotary damper is low, and the lid can be opened by a force corresponding to its weight.
When the rotatable member 5 rotates clockwise in the direction indicated by the arrow to close the lid from its open position, no gap is formed between the valve body 22 and the vane 16, and the fluid passage which has been produced is closed. Therefore, the flow of the fluid is greatly limited, and the rotary damper generates a high torque.
The conventional rotary damper has a clearance or play 103 that exists until the valve body 22 is brought into contact with the vane 16, closing the fluid passage. When the rotatable member 5 is rotated in the direction to close the lid, therefore, it takes the rotary damper a certain period of time before making a damping action based on the counterclockwise movement of the valve body 22 across the clearance 103. While the valve body 22 is moving counterclockwise across the clearance 103, the rotary damper does not produce a high torque and does not make a damping action. The range or period in which no damping action takes place is referred to as xe2x80x9cbacklashxe2x80x9d.
When the keyboard lid of a piano which incorporates the conventional rotary damper is slightly opened and then released, for example, since the rotary damper does not immediately produce a damping action due to the backlash, it is dangerous disadvantage that the keyboard lid may possibly be closed quickly.
To solve the above problem of the conventional rotary damper, the applicant of the present application has proposed a rotary damper free of backlash as disclosed in Japanese patent No. 2894596. As shown in FIG. 21 of the accompanying drawings, the proposed rotary damper includes a rotatable member 5 having a vane 16 which has a tip end of circular cross section, and a valve body 22 of C-shaped cross section fitted over and movably mounted on the tip end of the vane 16.
When the rotatable member 5 of the rotary damper shown in FIG. 21 rotates clockwise in the direction indicated by the arrow D, e.g., to open a lid connected to the rotary damper, the valve body 22 turns counterclockwise on the vane 16 due to a fluid resistance, a fluid passage 104 is produced between the valve body 22 and the inner circumferential surface of a cylindrical casing 2. When the rotary member 5 rotates counterclockwise, e.g., to close the lid, the valve 22 turns clockwise on the vane 16, closing the fluid passage 10. Therefore, the rotary damper can make a damping action relatively quickly.
With the above rotary damper, however, there is a certain limitation on efforts to reduce the magnitude of the backlash because the valve body is angularly moved by only the resistance that is caused to the fluid upon rotation of the rotating body.
As an improvement designed to eliminate the backlash of the above rotary damper, there has been proposed a rotary damper disclosed in Japanese laid-open patent publication No. 2000-120747. The proposed rotary damper has a spring mounted on a valve body for immediately closing a fluid passage to make a quick damping action.
Specifically, as shown in FIG. 22 of the accompanying drawings, the proposed rotary damper comprises a rotating body 5, a pair of vanes 16 projecting radially outwardly from the outer circumferential surface of the rotating body 5 and having respective recesses 102 defined in their tip ends, a pair valve bodies 22 each of a substantially L-shaped cross section having an arcuate portion 105 and a radial portion 106 and covering at least of respective tip end surfaces of the vanes 16, and a pair of springs 107 which are separate from the valve bodies 22 and interposed between the vanes and the valve bodies 22. Since the two vanes 16 and various components combined therewith are identical to each other, only one of the vanes 16 and components combined therewith will be described below. When the rotary damper is in a normal position shown in FIG. 22, the spring 107 urges the radial portion 106 into close contact with a side 108 of the vane 16 which faces in the direction to exert damping forces. When the rotatable member 5 rotates counterclockwise in the direction indicated by the arrow A, i.e., rotates idly, a tongue 110 of the spring 107 is deformed in a clockwise direction opposite to the direction indicated by the arrow A under the pressure of a viscous fluid, displacing the radial portion 106 away from the side 108.
The spring 107 includes a cross-sectionally channel-shaped fitting member 109 fitted in the recess 102, and the tongue 110 projects outwardly from the fitting member 109 and has an outer end fitted in a slot 111 defined in the arcuate portion 105 of the valve body 22. Therefore, the spring 107 is of a considerably complex structure.
If the rotary damper is small in size, then the space between the vane 16 and the valve body 22 for placing the spring 107 therein is also small in size. Therefore, the rotary damper cannot easily be assembled. The rotary damper is costly to manufacture because it is made up of a relatively large number of parts.
When the rotatable member 5 rotates idly in the direction indicated by the arrow A, the spring 107 is greatly deformed in the direction opposite to the direction indicated by the arrow A due to the resistance from the viscous fluid. After the rotary damper has been used over a long period of time, therefore, the spring 107 which is of a complex structure tends to be broken by fatigue at various locations on the fitting member 109 and the tongue 110. Particularly, the tongue 110 is liable to suffer elastic fatigue. Consequently, the rotary damper is likely to develop backlash after it has been used over a long period of time.
It is an object of the present invention to provide a rotary damper which will solve the problems of the conventional rotary dampers.
To achieve the above object, there is provided in accordance with the present invention a rotary damper comprising a casing having a fluid chamber filled with a fluid, a rotatable member disposed in the fluid chamber for rotation relative to the casing, a vane disposed on an outer circumferential surface of the rotatable member and extending in an axial direction thereof, the vane projecting toward an inner circumferential surface of the fluid chamber and having a first side and a second side opposite to the first side, a fluid passage for allowing the fluid to flow between the first side and the second side at or near a tip end of the vane, and a valve body mounted on the vane for selectively opening and closing the fluid passage, the valve body comprising a valve disposed in a position for closing the fluid passage and a spring for normally urging the valve in a direction to close the fluid passage, the valve and the spring being integrally formed, the arrangement being such that when the rotatable member rotates in a first direction, the valve opens the fluid passage against the urge of the spring under the pressure of the fluid on the first side of the vane, that when the rotatable member stops against rotation, the valve instantaneously closes the fluid passage under the urge of the spring, and that when the rotatable member rotates in a second direction, the valve keeps closing the fluid passage under the urge of the spring and the pressure of the fluid on the second side of the vane.
The valve body mounted on the vane for selectively opening and closing the fluid passage comprises the valve disposed in the position for closing the fluid passage and the spring for normally urging the valve in the direction to close the fluid passage. The valve and the spring are integrally formed. Therefore, when the rotatable member stops against rotation in the first direction, i.e., an idling direction not to produce a torque, the valve is automatically pressed against a side of the vane under the urge of the spring. Therefore, the fluid passage which has been open is instantaneously closed. When the rotatable member subsequently starts rotating in the second direction, i.e., a damping direction to produce a torque, the rotary damper immediately generates a high torque in the fluid chamber, quickly making a damping action.
The valve body which is made up of the valve and the spring that are integrally formed with each other is simple in structure. Even if the rotary damper is small in size with the clearance being small between the vane and the inner circumferential surface of the fluid chamber, the valve body with the spring function can easily be installed in the clearance. The rotary damper can easily be assembled, and can be manufactured at a greatly reduced cost as the number of parts of the rotary damper is greatly reduced.
The valve body is made of a springy material. Therefore, the valve body itself is of a simple structure, making the rotary damper inexpensive.
The springy material comprises a nonmetal spring material such as rubber, plastics, or the like. The valve body can thus be formed with ease, and has the advantage of-highly nonmagnetic and corrosion-resistant properties.
Alternatively, the springy material comprises a metal spring material such as steel, copper alloy, or the like. The valve body thus constructed allows the spring to produce a large urging force. If the valve body is made of spring steel, then since it has a large modulus of elasticity, the valve body has high elasticity, fatigue, and creep limitations. If the valve body is made of stainless steel, then it has the advantage of highly heat-resistant and corrosion-resistant properties. If the valve body is made of copper alloy for springs, then it has the advantage of highly nonmagnetic and corrosion-resistant properties.
The valve body comprises a leaf spring. The valve body in the form of a leaf spring is capable of bearing the resistance from the fluid, i.e., the pressure of the fluid with a large area. Therefore, when the rotatable member rotates in the first direction, i.e., in the idling direction, the fluid passage is easily opened, lowering the generated torque easily within a short period of time.
The vane has an axially extending slot defined in the tip end thereof by a first wall surface, a second wall surface confronting the first wall surface, and a bottom surface joining the first wall surface and the second wall surface to each other, the valve body being removably fitted in the slot, the valve fitted in the slot extending across the fluid passage to block the fluid passage and having at least a portion held against the first wall surface, the spring comprising a first extension extending from the valve, a curved portion extending from the first extension, and a second extension extending from the curved portion, the arrangement being such that the spring applies a urging force to the valve in a direction to close the fluid passage when a load is applied to the curved portion. Though the valve body is made of a single material, it may be constructed to have a spring function for urging the valve in the direction to close the fluid passage, and is not required to have a separate spring. The valve body with the spring function can thus be made highly simple in structure. The location where the valve body is installed can be produced simply by forming the axially extending concave portion, for example slot, in the tip end of the vane. The valve body which is of a highly simple structure can easily be fitted into the slot simply by compressing both of tongue portions, i.e. the valve or the first extension of the spring and the second extension toward each other and inserting them into the slot. Even if the clearance between the rotatable member and the inner circumferential surface of the fluid chamber is small due to a reduction in size of the rotary damper, the rotary damper can easily be assembled.
The fluid passage is defined between the tip end of the vane and the inner circumferential surface of the fluid chamber, the valve extending radially outwardly and having a tip end thereof held against the inner circumferential surface of the fluid chamber. When the rotatable member rotates in the first direction, i.e., in the idling direction, the valve bears the pressure of the fluid on the first side, so that the valve body is displaced away from the first wall surface, opening the fluid passage. When the rotatable member stops against rotation, the displaced valve body is immediately brought into close contact with the first wall surface under the urge of the valve or the first extension, instantaneously closing the fluid passage. When the rotatable member thereafter rotates in the second direction, i.e., the damping direction to produce a torque, the rotary damper produces a high torque in the fluid chamber, quickly making a damping action.
The valve has a ledge filling the space, serving as the fluid passage, between the tip end of the vane and the inner circumferential surface of the fluid chamber. When the rotatable member rotates in the first direction, i.e., in the idling direction, since the valve surely bears the pressure of the fluid on the first side, the valve body is immediately displaced away from the first wall surface, opening the fluid passage.
The tip end of the vane is held in contact with the inner circumferential surface of the fluid chamber, and the fluid passage is defined in the tip end of the vane. As it is sufficient for the valve body to have a length large enough to close the fluid passage at its valve, the dimensional accuracy of the valve body may be low.
The second extension has an end for limiting a range of movement of the valve when the valve is displaced away from the first wall surface and opens the fluid passage. Inasmuch as the range of movement of the valve is largely limited, any elastic deformation of the spring in the direction opposite to its urging direction is also largely limited. Accordingly, the spring is essentially free of elastic fatigue even when the rotary damper is used over a long period of time.
The valve has an apex seal function. When the rotatable member rotates in the second direction, i.e., the damping direction, the valve and the inner circumferential surface of the fluid chamber are held in close contact with each other. Therefore, the fluid is fully limited against flowing from the region where the valve and the inner circumferential surface of the fluid chamber are held in close contact with each other. The rotary damper is thus capable of generating a strong damping force upon rotation in the damping direction. The term xe2x80x9capex seal functionxe2x80x9d refers to a function for the pressure-bearing surface of the valve to bear the pressure of the fluid for thereby pressing the valve body toward the inner circumferential surface of the fluid chamber to press the tip end of the valve against the inner circumferential surface of the fluid chamber.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.